Spondylolisthesis correction apparatus and method

ABSTRACT

An apparatus and method are provided that allow for the realignment and stabilization of adjacent vertebrae. An implant of this invention both repositions adjacent vertebrae and remains in situ to maintain the new position. The implant has two halves which are interlocked such that they can slide horizontally with respect to each other. Movement of the implant halves and their respective positions are controlled by set screw within the implant. The implant includes radial anchors which fit into alignment slots made in the misaligned vertebra by the disclosed method. The set screws are used to advance the halves of the implant which in turn move the misaligned vertebrae back into correct positions. The correct position of the vertebrae is locked in place through a nut and a plate.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a divisional application claiming priority benefitfrom U.S. application Ser. No. 12/799,775 filed Apr. 30, 2012 whichclaims priority to U.S. application Ser. No. 11/821,717 filed Jun. 25,2007, now U.S. Pat. No. 7,744,649 issued Jun. 29, 2010.

FIELD OF INVENTION

The present invention relates generally to the correction ofspondylolisthesis and other spinal column injuries or deformities in thefields of neurosurgery and orthopedics. More specifically, the inventionis used for the stabilization of repositioned vertebral bodies.

BACKGROUND OF THE INVENTION

Spondylolisthesis is a medical condition in which one vertebra slipsforward in relation to an adjacent vertebra usually in the lumbar regionof the spine. This condition can cause symptoms that include pain in thelow back, thighs, and/or legs, muscle spasms, weakness, and/or tighthamstring muscles while in some cases only radiographic imaging revealsthe condition.

To correct this condition and other similar conditions of vertebraldislocation, the only effective long-term curative treatment isreconstructive surgery and fusion of the affected vertebra to itsadjacent neighbor. Vertebral fusion is generally accomplished by fixingapparatus to and between vertebrae. In addition to the stabilization andcorrection of spondylolisthesis, other spinal conditions may be:stabilization of fractures, correction of spinal deformities (e.g.scoliosis, kyphosis), stabilization and correction of degenerativespinal lesions and narrow spinal canal, reconstruction after tumorresection, and secondary spinal surgery.

The novel method and implant discussed herein allows for the correctionof spondylolisthesis by movement of the vertebrae into better alignmentwhile maintaining stabilization of the vertebrae in the new position inorder for the spinal fusion to be completed by ossification.Specifically, the implant is used to move the vertebrae into apost-surgical position and keep the vertebrae in the post-surgicalposition during the ossification process.

Roggenbuck in U.S. Pat. No. 6,491,695 discloses the use of an apparatusand method for aligning vertebrae which involves creating a helicalthreaded surface in endcaps of the vertebrae and then threading apositioning device into position to align the vertebrae. Once thevertebrae are positioned, the positioning device is removed and animplant is inserted to maintain the vertebrae in position.

Ray in U.S. Pat. No. 6,582,431 discloses the use of an expandablenon-threaded spinal fusion device which requires the vertebrae to bemoved into correct position before the device can be inserted andimplanted.

Betz in U.S. Pat. No. 6,533,791 discloses a device for stabilization ofthe lumbar spinal column which requires cutting helical thread marksinto the vertebrae that are to be repositioned and then installing animplant to maintain the position. The repositioning device does not stayin the body after the surgery but instead an implant must be inserted tomaintain the repositioning.

Therefore, there is a need in the art to combine an implant with arepositioning device in order to reduce the possible repositioning ofthe vertebrae. There is a further need in the art to provide foradjustment of the vertebrae after an implant has been installed.

SUMMARY

Disclosed is an apparatus and method for aligning vertebrae due toslippage of the vertebrae relative to each other. To this end, a methodand apparatus is disclosed for placing a novel implant between twovertebrae which will move the vertebrae into proper alignment andmaintain that alignment until ossification can occur. The implantdisclosed is left in situ once the vertebrae have been repositioned. Theimplant disclosed also provides support for the effected vertebraesuperior to that of previous methods known in the prior art. The implantalso allows for fine adjustments and post implantation adjustments ofthe vertebrae superior to that of the prior art.

The disclosed method includes approaching the vertebra anteriorly andremoving a portion of vertebral disk between the misaligned vertebrae.Known interbody spacers are then inserted between the vertebrae untilthe proper restorative height is achieved. The spacers are removed and adistractor is placed between the vertebrae in order to guide thesubsequent placement of the implant. A novel gate is inserted over anovel distractor to properly guide a novel saw mechanism to cut into thevertebrae at precise locations and allow for the insertion of a novelimplant. Different gates are provided depending on the necessaryrestorative height to be achieved and amount of slip between thevertebrae.

The disclosed implant has two halves which include a dovetail groovesystem which locks the two halves together but allows them to slide withrespect to each other along their longitudinal axis. The implant hasradial anchors which extend from each half and which fit into slots inthe vertebrae cut by the saw. The implant includes a drive bolt whichengages the two halves and which, when turned, slides one half of theimplant in relation to the other. The advancing halves of the implantcarry the radial anchors with them that align the vertebrae. Dependingon the amount of slip between the vertebrae and the necessaryrestorative height, different sized implants and associated tools may beused.

The implant is inserted through a distractor by use of an inserter. Thehalves of the implant are aligned so that the radial anchors correspondto slots made in the misaligned vertebrae. The implant is rotated intoplace by the inserter such that the radial anchors fit securely in theslots previously made by the saw in the vertebrae. The distractor isthen removed.

In the case of anterior listhesis of the superior vertebra, the drivebolt of the implant is then rotated so that the upper half of theimplant is advanced posteriorly. The superior vertebra is pulledposteriorly with respect to the inferior vertebra by the movement of theupper half of the implant with respect to the lower half.

The position of the implant is locked into place by use of anarticulating combination of a nut and a plate, thereby maintainingalignment of the vertebrae. The nut and plate can be removed, allowingfor post-surgical adjustment of the implant.

BRIEF DESCRIPTION OF DRAWINGS

The disclosed inventions will be described with reference to theaccompanying drawings, which show important sample embodiments of theinvention and which are incorporated in the specification hereof byreference, wherein:

FIG. 1 is a side view of a section of human spine characterized by aspondylolisthesis condition.

FIG. 2 is an isometric view of a distractor of a preferred embodiment ofthe invention.

FIG. 3A is an isometric view of an impactor of a preferred embodiment ofthe invention.

FIG. 3B is an isometric view of an impactor in conjunction with adistractor of a preferred embodiment of the invention.

FIG. 4 is a side view of a section of a human spine with the distractorin place between vertebrae.

FIG. 5A is a partial isometric view of a gate of a preferred embodimentof the invention.

FIG. 5B is a plan view of a gate of a preferred embodiment of theinvention.

FIG. 5C is an elevated view of a gate of a preferred embodiment of theinvention.

FIG. 6 is an exploded isometric view of a saw of a preferred embodimentof the invention.

FIG. 7A is a partial plan view of the relational section of the saw of apreferred embodiment of the invention.

FIG. 7B is a partial isometric view of the spindle shaft of a preferredembodiment of the invention.

FIG. 7C is a partial side view of the spindle shaft of a preferredembodiment of the invention.

FIG. 8A is an end view of the saw with the saw blade in a loweredposition of a preferred embodiment of the invention.

FIG. 8B is an end view of the saw with the saw blade in a raisedposition of a preferred embodiment of the invention.

FIG. 9 is a cut away side view of section of a human spine with thedistractor, gate, and saw in place between the vertebrae.

FIG. 10 is an exploded isometric view of the implant of a preferredembodiment of the invention.

FIG. 11 is an isometric view of the implant of a preferred embodiment ofthe invention.

FIG. 12 is an isometric view of the implant in an extended position of apreferred embodiment of the invention.

FIG. 13A is an end view of the inserter of a preferred embodiment of theinvention.

FIG. 13B is an isometric view of the inserter of a preferred embodimentof the invention.

FIG. 14 is a partial isometric view of the inserter and the implant of apreferred embodiment of the invention prior to attachment.

FIG. 15 is an isometric view of a guide block of a preferred embodimentof the invention.

FIG. 16 is a cut away side view of a section of a human spine and animplant during positioning by an inserter of a preferred embodiment ofthe invention.

FIG. 17 is a cut away side view of a section of a human spine and animplant in place prior to the alignment of the vertebrae.

FIG. 18 is an isometric view of a nut of a preferred embodiment of theinvention.

FIG. 19A is an isometric view of a plate of a preferred embodiment ofthe invention.

FIG. 19B is a cut away side of a plate of a preferred embodiment of theinvention.

FIG. 20 is a cut away side view of a section of a human spine with animplant in a retracted position and a nut and a bolt in place.

FIG. 21 is a cut away side view of a saw in an alternate saw embodiment.

FIG. 22A is a cut away side view of the end of saw in an alternateembodiment of the invention.

FIG. 22B is an end view of the end of an alternate saw embodiment.

FIG. 23A is a top view of the top of the chuck of an alternate sawembodiment.

FIG. 23B is a partial cut away side view of the chuck of an alternatesaw embodiment.

FIG. 24A is a side view of an implant in another embodiment of theinvention.

FIG. 24B is an end view of an implant in another embodiment of theinvention.

FIG. 25 is an isometric view of an impactor in conjunction with adistractor of another embodiment of the invention.

DETAILED DESCRIPTION

FIG. 1 is an illustration of a lumbar spine in a patient who hascontracted spondylolisthesis. The vertebrae 10 are separated byvertebral disk 50. As a result of advanced spondylolisthesis, superiorvertebra 20 slips forward in relation to the next inferior vertebra 40and causes distended disk 70. To repair slippage of the vertebrae,superior vertebra 20 and inferior vertebra 40 are realigned and fusedtogether. To accomplish this, a portion of distended disk 70 is removedand replaced with an implant which maintains realignment and supportsthe spine until ossification occurs whereby superior vertebra 20 andinferior vertebra 40 are permanently fused.

In order to assure proper alignment, a magnetic resonance image (“MRI”)or plain lateral radiographs are used to observe the supine position tomeasure the severity of the spondylolisthesis condition prior tosurgery. The restorative height of the interbody space after partialremoval of distended disk 70 and the necessary amount of re-alignmentcan be estimated by review of the MRI or plain lateral radiographs. Theimplant size can be determined by the estimates.

The present invention uses the anterior surgical approach to the lumbarspine in order to reach the vertebrae that will receive the implant. Theanterior surgical approach to the lumbar spine is understood in the artand is not discussed in detail here.

Referring still to FIG. 1, once the lumbar spine is exposed to thesurgeon, superior vertebra 20, inferior vertebra 40, and distended disk70 are located and identified. A standard marking pin known in the artis inserted into distended disk 70 at the putative midline and left inplace.

The implant should be optimally placed at the midline in the sagitalplane. Lateral radiographs or x-rays are utilized to confirm theappropriate surgical level and anterior-posterior x-ray imagingdemonstrates the midline relative to the marking pin. Once confirmed,the midline of distended disk 70 is marked on distended disk 70 by useof generally accepted marking means. The marking pin is then removed.

Portion of distended disk 70 is removed. Boundaries of generousrectangular annulatomy are created in distended disk 70 by use ofscalpel. The size of the annulatomy will depend upon the size of theimplant and allows additional space on either side of implant to allowinterbody arthodesis on both sides of implant after implant is deployed.The width of annulatomy will be in the range of between about 2 cm andabout 5 cm. Portion of distended disk 70 within the boundary ofannulatomy is removed by use of rongeurs and curettes.

Vertebral endplate preparation is performed in standard fashion as knownin the art while maintaining cortical endplate integrity centrally.Anterior osteophytes may also be removed from the ventral aspect of thevertebral bodies during this stage of the surgery.

In order to gain the appropriate restorative height between superiorvertebra 20 and inferior vertebra 40, sequentially larger interbodyspreaders are impacted into the rectangular annulotomy in distended disk70 until optimal height restoration is achieved. Interbody spreaders areknown in the art. When optimal height restoration is achieved, interbodyspreaders are removed and appropriate height distractor 110 is inserted.

FIG. 2 illustrates one embodiment of distractor 110. Distractor 110 ismade of titanium, stainless steel, or other commercially availablematerial which is easily sterilized. Rigid plastics can be used such aspolyvinyl chloride (PVC) in disposable embodiments. Distractor 110 isrectangular in cross-section and includes hollow distractor channel 115.Distractor channel 115 is rectangular in cross-section and runs thelength of distractor 110 along distractor body longitudinal axis 1100.The dimensions of distractor 110 vary depending on the optimal heightrestoration to be achieved, but height of distractor 110 shouldgenerally range between about 0.5 cm and about 1.5 cm and the width ofdistractor 110 should range between about 2 cm and about 5 cm. Thelength of distractor 110 is between about 30 cm and about 60 cm. Thethickness of walls of distractor 110 should range between about 1 mm andabout 5 mm depending on the material of construction to achieve a rigidstructure. The dimensions of distractor channel 115 should range betweenabout 0.4 cm and about 1.4 cm high, about 1.9 cm and about 4.9 cm wide.

Posterior end of distractor 110 contains distractor arm 117 anddistractor arm 118. Distractor arm 117 extends longitudinally from side80 of distractor 110. Distractor arm 117 includes distractor point guide246 having angled surfaces 253 and 254. Opposing angled surfaces 253 and254 is distractor stop 119. Distractor arm 118 extends longitudinallyfrom the side 81 of distractor 110 and includes distractor point guide256 having rounded surfaces 258 and 255. Opposing rounded surfaces 258and 255 is distractor stop 122. The height of distractor arm 117 anddistractor arm 118 are approximately the same as the height ofdistractor 110. The width of distractor arm 117 and distractor arm 118are between about 0.5 mm and about 1 mm. The width of the distractorarms should provide rigidity with respect to the body of the distractor.Distractor arm 118 and distractor arm 117 form implant hollow 130. Endgap 120 is formed at the forward end of implant hollow 130. Thepreferred design of end gap 120 is between about 1.7 cm and about 4.7cm. Distractor stop 122 and distractor stop 119 are between about 0.5 mmand about 2 mm in length.

Torque handle 235 is rigidly mounted to distractor body 99. Torquehandle 235 is generally in the range of about 2 cm to about 5 cm inlength with a diameter in the range of about 0.5 cm to about 2 cm. Thepreferred location of torque handle 235 is approximately between ¼ to ½from the anterior end 111 of distractor 110. A set of distractorgraticules 135 are etched at 1 mm intervals on the side of distractor110 along the outside of distractor arm 118 and distractor arm 117.

In the preferred embodiment, the cross-sectional height and width ofdistractor 110 may vary. In its preferred use, a set of variable heightdistractors is provided so that the distractor height which matches thevertical distance between the vertebrae may be used during surgery. Thepreferred set of heights preferably varies in one millimeter incrementsbetween about 5 mm and about 2 cm.

FIG. 3A illustrates the preferred embodiment of impactor 140. Impactor140 includes impactor handle 170 which is cylindrical with a diameter inthe range of about 0.3 cm and about 2 cm and is centered along theimpactor longitudinal axis 1400. The length of impactor handle 170ranges between about 5 cm and about 25 cm. In one embodiment, impactorhandle 170 is etched with impactor centerline 165 across its diameter.Impactor centerline 165 is parallel to the latitudinal axis 160 ofimpactor 140.

Impactor body 161 is formed integrally with impactor handle 170.Impactor body 161 is rectangular in cross-section and sized to fitwithin distractor channel 115 without excessive play. In the preferredembodiment, the impactor body is sized to allow for approximately 0.3 mmplay between the exterior of the impactor body and the distractorchannel.

Angled section 141 extends from impactor handle 170 to impactor body 161at an angle between about 25 and about 65 degrees. Angled section 141serves to center the impactor handle with respect to the impactor bodyand distribute impact loads from the impactor handle to the impactorbody as will be further described. The preferred length of impactor body161 should range between about 30 cm and about 45 cm. The posterior endof impactor body 161 includes impactor seat 150 integrally formed withimpactor body 161. Impactor seat 150 is sized and shaped to fit withinend gap 120 shown in FIG. 2. Impactor seat 150 has rounded surface 155.On either side of impactor seat 150 are stop surface 152 and stopsurface 153. Impactor 140 is preferably made from titanium, stainlesssteel, or other materials which are readily sterilized or from a rigidplastic such as PVC which may be disposed of after use.

Other cross-sectional shapes of the impactor and distractor are alsoacceptable, such as elliptical, as long as the impactor fits inside thedistractor channel such that it can move longitudinally in distractorchannel 115 without rotation and without significant “play” or angulardisplacement.

In use, impactor 140 is placed inside distractor channel 115, such thatimpactor seat 150 fits into end gap 120 as shown in FIG. 3B. Impactorcenterline 165 is aligned with the anatomical midline marked previously.Distractor 110 and impactor 140 are aligned with the anatomical midlineand inserted into the rectangular anriulatomy in distended disk 70. Amallet is used to tap impactor 140 at striking end 145 and movedistractor 110 into the midline sagital plane under fluoroscopicguidance until posterior edge of distractor 110 reaches the dorsalepiphyseal ring on the ventrally superior vertebra 20. Impactor 140 isthen withdrawn from distractor channel 115 and distractor 110 is left insitu.

In the preferred embodiment, impactor 140 is also provided in a set ofvariable sizes to match the set of variable sizes of distractor 110, aspreviously described.

FIG. 4 shows distractor 110 in situ between superior vertebra 20 andinferior vertebra 40. Distractor 110 is between superior vertebra 20 andinferior vertebra 40. Once in position, distractor graticules 135 areused to gauge the amount of slip existing between superior vertebra 20and inferior vertebra 40.

FIGS. 5A, 5B, and 5C illustrate an embodiment of gate 180. Gate 180 hasa gate body 223 bordered by side wall 271, bottom side 269, side wall284 and top side 268. The gate body extending along gate longitudinalaxis 1200 also includes saw end 249 and distractor end 251. In thepreferred embodiment, gate 180 has a length of between about 5 cm andabout 10 cm along gate longitudinal axis 1200, a width of between about2.2 cm and 5.8 cm along gate latitudinal axis 1210, and a height ofbetween about 0.7 cm and about 2.9 cm.

Gate 180 is provided with saw guide 220 and saw guide 230. Saw guides220 and 230 are a pair of slots which are situated approximately thecenter of top side 268 to the center of side wall 284, encompassingapproximately ¼ of the perimeter of gate body 223. The pair of sawguides are in parallel planes. Saw guide 220 and saw guide 230 terminatein handle guide 257. Handle guide 257 forms a slot generally in thecenter of side wall 284. Handle guide 257 is provided with handle stop252. The width of saw guides 220 and 230 and handle guide 257 in thepreferred embodiment is between about 0.5 cm and 1.5 cm.

Gate body 223 is also provided with saw guide 200 and saw guide 210. Sawguides 200 and 210 are a matched pair of slots which are situatedapproximately the center of bottom side 269 to the center of side wall271, encompassing approximately % of the perimeter of gate body 223. Thepair of saw guides are in parallel planes. Saw guide 200 and saw guide210 terminate in handle guide 240. Handle guide 240 forms a slotgenerally in the center of side wall 271. Handle guide 240 is providedwith handle stop 242. The width of saw guide 200, saw guide 210 andhandle guide 240 in preferred embodiment is between about 0.5 cm andabout 1.5 cm.

Saw guide 220, saw guide 230 and handle guide 257 are ductedlyconnected. Saw guide 220 and saw guide 230 are on centers of betweenabout 0.5 cm to 3.5 cm in the preferred embodiment. Further, saw guide220 is approximately 0.9 cm from saw end 249.

Saw guide 210, saw guide 200 and handle guide 240 are ductedlyconnected. Saw guide 210 and saw guide 200 are on centers of betweenabout 0.5 cm to 3.5 cm in the preferred embodiment. Further, saw guide210 is approximately 1.9 cm from saw end 249.

Gate body 223 is further provided with interior channel 195 which islongitudinally centered within gate body 223. Interior channel 195includes saw entrance 247. Saw entrance 247 in the preferred embodimenthas dimensions slightly larger than guide body 310 which will bedescribed in more detail with respect to FIG. 6. The diameter of sawentrance 247 is maintained by interior channel 195 from saw entrance 247until gate lip 185. At gate lip 185, interior channel 195 increases inheight and width to accommodate the exterior of distractor 110. Thedimensions of interior channel 195 remain constant from gate lip 185 todistractor end 251 terminating in distractor entrance 248.

In one embodiment, gate 180 can also include raised indicator arrow 245or other visual aid or tactile indicator to indicate which end of gate180 is to be inserted over distractor 110.

In the preferred embodiment, many gates are provided in a kit duringsurgery. The gates each have saw guides that are spaced apart atdifferent lengths with respect to the top and the bottom of each gate.The different spacings correspond to different distances that thevertebrae have slipped. In one preferred embodiment, in the less severecases, saw guides 230 and 220 will be offset from saw guides 200 and 210by about 1 mm. The offset between saw guides 230 and 220 and saw guides200 and 210 will increase by 2 mm increments. In more severe cases, theamount of slip will be more pronounced and the offset can beapproximately 20 mm. Position of saw guides 200 and 210 on gate 180 willstay constant. The gates also vary in height to match the variableheight of the distractor.

Referring now to FIGS. 6 and 7A, 7B, and 7C, an embodiment of saw 250can be seen. Saw 250 includes saw handle 260 to conical section 262.Conical section 262 is connected to handle post 265. Handle post 265integrally supports saw guide post 270. Saw guide post 270 isperpendicular to the longitudinal axis 1250 of saw 250. Handle post 265includes abutment surface 272 narrows to the diameter of spindle shaft273. Abutment surface 272 connects spindle shaft 273 with blade seatingshoulder 275. Blade seating shoulder 275 is flat surface 276 andsemicircular section 277. Blade seating shoulder 275 is connected tobolt 295. Bolt 295 has threaded section 296 which is directly adjacentto flat surface 276 and semicircular section 277. Bolt 295 has athreaded section 296 and a flat surface 297.

Saw 250 includes guide body 310. Guide body 310 includes a rectangularsection 311 and an angular section 312. Rectangular section 311 in thepreferred embodiment is sized to fit within saw entrance 247 as shown inFIG. 5B and distractor channel 115 shown in FIG. 2. The rectangularsection tolerance must be such that rectangular section 311 slideslongitudinally with respect to distractor channel 115 and interiorchannel 195 without significant angular play about the longitudinalaxis. In the preferred embodiment, these tolerances are approximately0.3 mm. Angular section 312 connects to flat surface 313. Guide body 310also includes spindle hole 301 which traverses the longitudinal axis ofguide body 310 and is sized to fit around spindle shaft 273. Spindlehole 301 is sized to allow rotation with respect to spindle shaft 273.

Rectangular section 311 includes spacer 300, saw alignment stop 281 andsaw alignment stop 279. As can be seen best in FIG. 7A and FIG. 6, sawalignment stop 281 includes a horizontal surface 282. Saw alignment stop279 includes vertical surface 283.

When assembled, saw 250 provides for 90 degrees rotation of saw handle260 with respect to guide body 310. Thrust bearing 302 rests adjacentabutment surface 272. Guide body 310 rests on spindle shaft 273 viaspindle hole 301. Flat surface 313 is adjacent angular section 312 andthrust bearing 302 providing a bearing surface between abutment surface272 and flat surface 313. Thrust bearing 278 resides around semicircularsection 277 of blade seating shoulder 275 adjacent vertical end 315 ofrectangular section 311. Locking hole 285 of saw blade 280 is adjacentflat surface 276 and semicircular section 277 of blade seating shoulder275. Locking hole 285 includes flat surface 316 which when brought intocontact with flat surface 276, prevents rotation of saw blade 280 withrespect to blade seating shoulder 275, consequently, with respect to sawhandle 260. Lock nut 290 is threaded onto threaded section 296 of bolt295. Flat surface 276, flat surface 316 and saw alignment stop 281 areparallel with the axis of saw guide post 270. In one embodiment, sawblade longitudinal axis 1260 of saw blade 280 is also parallel with theaxis of saw guide post 270.

Saw 250 and all its components are made from titanium, stainless steel,or other material which is used with surgical tools and equipment. Inthe preferred embodiment, rectangular section 311 of saw 250 is providedin several sizes in a set of several sizes to match the sizes of thedistractor 110, as previously described. Alternatively, a set of severalsaws 250 is provided, each having a rectangular section 311 whosecross-section is sized to match the distractor channel 115 of the set ofdistractors 110. In addition, a set of blades may be provided eachhaving different dimensions to achieve different lumbar dimensions.

FIGS. 8A and 8B are end views of saw 250. FIG. 8A illustrates saw blade280 in lowered position. In lowered position, saw blade 280 is flushwith guide body 310. FIG. 8B illustrates saw blade 280 in raisedposition. In raised position, saw blade 280 is perpendicular to guidebody 310.

In the preferred embodiment, saw blade 280 is between 0.9 cm and 4.9 cmlong with a width of between 1 mm and 5 min. Saw blade 280 has a flatbottom and two curved ends 303 and 305. Saw blade 280 includes a lockinghole 285 of approximate diameter and shape as bolt 295. Curved end 305includes saw teeth 304 having a height of about 0.5 mm and about 1.5 mm.Saw blade 280 also includes notches 317 and 318. As shown in FIG. 8B,saw blade 280 in its raised position rests adjacent vertical surface 283which prevents it from rotating counterclockwise. In lowered position,as shown in FIG. 8A, notch 318 rests adjacent horizontal surface 282 andprevents rotation of the saw blade clockwise.

Referring now to FIG. 9, in use, gate 180 is placed over the anteriorend of distractor 110 and advanced until anterior end 111 rests againstgate lip 185. Saw 250 is placed in lowered position. Rectangular section311 is placed in interior channel 195 and advanced through distractorchannel 115 until spacer 300 reaches distractor stop 122 or saw guidepost 270 reaches handle stop 242.

In use, the saw is used to make two sets of receiving notches in theupper and lower vertebrae that correspond to the positions of the sawguides. More particularly, saw 250 is retracted until saw guide post 270is directly adjacent saw guide 230. Saw handle 260 is rotated clockwise90 degrees such that saw guide post 270 advances through saw guide 230on gate 180. Rotation of saw handle 260 will rotate saw blade 280causing it to cut into superior vertebra 20 thereby forming a slot 900.Distractor torque handle 235 is grasped to apply counter torque andprevent rotation of the saw from displacing distractor 110 angularlywith respect to the effected vertebrae. Saw handle 260 is then rotatedcounterclockwise positioning saw guide post 270 in handle guide 257. Saw250 is then extracted such that saw guide post 270 is adjacent saw guide220. Saw handle 260 is then rotated clockwise 90 degrees such that sawguide post 270 advances into saw guide 220. Rotation of saw handle 260rotates saw blade 280 thereby cutting into superior vertebra 20 andforming slot 902. Saw guide post 270 is then rotated counter-clockwiseso that saw guide post 270 resides in handle guide 257.

Saw blade 280 is placed in its lowered position. Saw 250 is then removedfrom distractor channel 115 through interior channel 195. Saw 250 isthen rotated 180 degrees about its axis and rectangular section 311replaced is in interior channel 195 of gate 180. Saw 250 is furtherreinserted into distractor channel 115.

Saw guide post 270 is adjacent saw guide 210. The saw handle is rotatedclockwise 90 degrees such that saw guide post 270 enters saw guide 210.Rotation of saw handle 260 consequently rotates saw blade 280 exposingsaw teeth 304 to inferior vertebra 40 thereby cutting into inferiorvertebrae 40 thereby forming slot 903. Distractor torque handle 235 isused to apply counter torque and prevent the saw rotation fromdisplacing distractor 110. Saw handle 260 is then rotated clockwise suchthat saw guide post 270 advances through the saw guide and into handleguide 240. Saw 250 is then extracted such that saw guide post 270advances through handle guide 240 until it is adjacent saw guide 200.Saw handle 260 is then rotated 90 degrees such that saw guide post 270advances into saw guide 200. The rotation of saw handle 260 rotates sawblade 280 causing a second cut into inferior vertebra 40 thereby formingslot 904.

Saw 250 is removed through distractor channel 115 and interior channel195. Gate 180 is then removed from the anterior end of distractor 110.

Slots 900, 902, 903 and 904 in superior vertebra 20 and inferiorvertebra 40 are substantially consistent with the spacing on gate 180between saw guides 200, 210, 220, and 230, respectively.

The novel implant is then prepared to be inserted.

Referring to FIGS. 10, 11 and 12, implant 320 is described. Implant 320is comprised of two semi-cylindrical halves, upper half 340 and lowerhalf 330. Upper half 340 extends along an upper half longitudinal axis1310 and includes parallel radially exposed and planar radial anchors264 and 261 extending perpendicularly from an upper half outer surface1340. The radial anchors are integrally fanned with upper half 340.Radial anchor 264 further includes curved surface 266. Radial anchor 261includes curved surface 263.

Lower half 330 extends along a lower half longitudinal axis 1300 andincludes two parallel planar radial anchors 370 and 371. Radial anchors370 and 371 are integrally formed with lower half 330 extendingperpendicularly from a lower half outer surface 1330. Radial anchor 370includes curved surface 372. Radial anchor 371 includes curved surface373.

Upper half 340 includes upper threaded collar 345. Lower half 330includes lower threaded collar 355. The exterior of the upper halfincludes index marks 360. Index marks 360 correspond with index marks361 on lower half 330.

Upper half 340 includes upper channel 380 which is threaded with a setof channel threads. Lower half 330 includes lower channel 390. Lowerchannel 390 is not threaded. Upper half 340 is joined to lower half 330with a mating interconnection between dovetail guide 386 and dovetailguide 385 found on upper half 340 and dovetail slot 396 and dovetailslot 395, respectively, located on lower half 330.

Lower half 330 includes set screw stop 400 integrally formed with lowerhalf 330 and residing within lower channel 390. Set screw stop 400 issolid plug which fills lower channel 390 beyond end of set screw 350.Set screw 350 includes spanner slot 405 and a set of set screw threads351.

Lower half 330 includes set screw step 392. Set screw step 392 extendsinto upper channel 380 and in upper half 340 and lower channel 390 inlower half 330. Set screw step 392 decreases diameter of upper channel380 and lower channel 390 by approximately 2 mm.

As can best be seen in FIG. 12, when assembled, upper half 340 and lowerhalf 330 of implant 320 are engaged in a sliding relationship providedby the dovetail guides 385 and 386 residing in dovetail slots 395 and396. As can be seen in FIG. 11, when assembled, upper half 340 and lowerhalf 330 form implant body 346. Radial anchor 264 is aligned with radialanchor 370. Radial anchor 261 is aligned with radial anchor 371.Furthermore, upper threaded collar 345 and lower threaded collar 355 arealigned and form a cylindrical threaded attachment collar 356.

In use, set screw 350 can be rotated either counter-clockwise orclockwise within lower channel 390 and upper channel 380. The set screwis retained in position by set screw stop 400 and set screw step 392. Asset screw 350 is rotated, set of set screw threads 351 engage the set ofchannel threads on upper channel 380 and slide upper half 340 withrespect to lower half 330. As upper half 340 and lower half 330 aredisplaced, radial anchors 264 and 261 are displaced with respect toradial anchors 370 and 371 along the longitudinal axis of implant 320.The set of channel threads and set of set screw threads 351 have apre-determined relationship to allow upper half 340 to move apre-determined distance in relation to lower half 330 when set screw 350is rotated a pre-determined angle of rotation

Implant 320 in the preferred embodiment is made from titanium, stainlesssteel, alloys such as titanium allow, or other materials which areeasily sterilizable. Implant 320 or parts thereof, may also be made fromcomposite materials such as synthetic bone. Some composites or syntheticbone products include demineralized bone matrix, collagen, ceramics,cements, and polymers, such as silicone and some acrylics and includeproducts such as Vitoss, Cortoss, Rhakoss, Pro Osteon, and Gu-Bang.

In the preferred embodiment, implant body 346 is between about 0.5 cm toabout 2.5 cm in diameter and between about 2.0 cm and about 4.5 cm inlength. In the preferred embodiment, cylindrical threaded attachmentcollar 356 is between about 0.4 to about 2.4 cm in diameter and betweenabout 0.5 and 2.0 cm in length. In the preferred embodiment, radialanchors 264, 261, 370 and 371 have a height (as measured from the centerplane of the implant) of between about 0.5 cm and about 3.5 cm with anaspect ratio of ½ to 1½ between radial anchors 264, 261, 370, and 371and diameter of implant body 346.

In the preferred embodiment, upper half 340 includes exactly two radialanchors and lower half 330 includes exactly two radial anchors. However,in other embodiments, the upper half and lower half of the implant mayinclude more or less than two radial anchors. Furthermore, the upperhalf and lower half of implant 320 do not necessarily need to includethe same number of radial anchors. In embodiments which includedifferent numbers of radial anchors, it will be understood by thoseskilled in the art that the same number of saw guides must be includedon gate 180 in order to correspond with the number and orientation ofthe radial anchors.

FIGS. 13A and 13B illustrate inserter 430. Inserter 430 includes upperhalf 440 and lower half 450. Upper half 440 includes upper hexagonalsection 441 and upper cylindrical section 442 having upper longitudinalaxis 1600. Within upper cylindrical section 442 resides upper dovetailguide 454. Adjacent upper dovetail guide 454 is implant channel 446.Implant channel 446 includes locking thread 445.

Lower half 450 includes lower hexagonal section 451 and lowercylindrical section 453 having lower longitudinal axis 1610. Lowercylindrical section 453 includes lower dovetail channel 452. Upperdovetail guide 454 fits within lower dovetail channel 452 and allows forsliding movement between upper half 440 and lower half 450. As can bestbe seen in FIG. 13B, when upper half 440 and lower half 450 areassembled, inserter 430 assumes an outer circular perimeter. In thepreferred embodiment, this outer circular perimeter is sized to fitwithin distractor channel 115, shown in FIG. 2, with sufficientclearance to allow for rotation of inserter 430. Further, in thepreferred embodiment, the hexagonal shape of upper half 440 and lowerhalf 450 and inserter 430 is sized to allow for rotation with a toolsuch as a spanner wrench. In the preferred embodiment, the length ofinserter 430 is sufficient to span the length of distractor body 99.

Locking thread 445 is sized to mate with upper threaded collar 345 onimplant 320 as shown in FIGS. 10, 11 and 12.

Referring to FIG. 15, guide block 460 will be described. Guide block 460includes guide block bottom 465 and guide block top 475. Guide block 460also includes guide hole 470 which is centrally located within the guideblock and spans its length along guide block longitudinal axis 1450.Guide block bottom 465 is sized to fit within distractor channel 115.Guide block top 475 is sized so that it will not fit within distractorchannel 115 but rather abut anterior end 111 of distractor body 99 (asshown in FIG. 2).

In use, inserter 430 is used to place the implant in position betweenthe affected vertebra and rotated into position. More particularly thento implant the implant, the amount of offset calculated according to theradiograph is reduced to a number of millimeters. The implant isadjusted using upper adjustment index marks 360 and lower adjustmentindex marks 361 to an offset position using set screw 350. The amount ofoffset can be observed by observing the offset between index marks 360and 361. In an alternate embodiment, the offset can be derived bycalculating the number of rotations of the set screw and multiplying bythe pitch of the threads. In an alternate embodiment, the pitch of thethreads is set to a convenient number so that a single rotation of theset screw results in a predetermined movement of the upper and lowerhalves, such as 1 mm for example. An example of an offset position isshown in FIG. 12.

In use, inserter 430 is assembled and its cylindrical section is guidedinto and through guide hole 470 until guide block top 475 reaches thehexagonal section of the inserter.

Implant 320 is then connected to inserter 430 as shown in FIG. 14.Locking thread 445 of inserter 430 is engaged with upper threaded collar345 of implant 320. Inserter lower half 450 is advanced towards implant320 whereby dovetail guides 386 and 385 of implant 320 are engaged bylower dovetail channel 452 on inserter 430 thereby securing implant 320to inserter 430.

Referring now to FIG. 16, the process of inserting implant 320 into theaffected vertebra will be described. As previously described, distractor110 is in position between superior vertebra 20 and inferior vertebra40. Implant 320, while attached to inserter 430 is oriented and placedwithin distractor channel 115. Implant 320 is placed in distractorchannel 115 with radial anchors 264 and 261, 370 and 371 positioned sothat clockwise rotation of the implant will result in radial anchor 264and 261 encountering superior vertebra 20 and radial anchor 370 and 371encounter inferior vertebra 40. Using the hexagonal section of inserter430, implant 320 is advanced within distractor channel 115 a sufficientdistance to allow guide block bottom 465 to be inserted into distractorchannel 115. Guide block bottom 465 is advanced within distractorchannel 115 until guide block top abuts anterior end 111 of distractorbody 99.

Implant 320 is then advanced within distractor channel 115 until thehexagonal section of inserter 430 abuts guide block top 475.

The dimensions of guide block top 475 and cylindrical section ofinserter 430 are such that when the hexagonal section of the inserterabuts guide block top 475, implant 320 is in proper position in relationto slots 900, 902, 903 and 904 such that radial anchor 264 is adjacentslot 900, radial anchor 261 is adjacent slot 902, radial anchor 370 isadjacent slot 904 and radial anchor 371 is adjacent slot 903.

Inserter 430 is then rotated 90 degrees clockwise such that the radialanchors are rotated into position in the slots in their respectivevertebrae.

Once in position, implant 320 is released from inserter 430.

The diameter of inserter guide hole 470 should provide sufficientclearance for rotation and transition of cylindrical portion of inserter430 without excessive play. In the preferred embodiment, the diameter ofguide hole 470 should not exceed the diameter of the cylindrical sectionof inserter 430 by more than 0.1 mm.

To release implant 320 from inserter 430, inserter lower half 450 isretracted anteriorly past superior locking thread 445 and disengagesfrom lower dovetail channel on lower cylindrical section 453 of theinserter. Inserter 430 is rotated 180 degrees such that upper threadedcollar 345 is disengaged from locking thread 445 on implant channel 446on the inserter. Inserter 430 and guide block 460 are then removed fromdistractor 110.

Distractor 110 is then removed from between superior vertebra 20 andinferior vertebra 40 by pulling anteriorly.

FIG. 17 illustrates the positioning of implant 320 between superiorvertebra 20 and inferior vertebra 40 after distractor 110 has beenremoved. Upper half 340 is adjacent superior vertebra 20, radial anchor264 is located in slot 900, radial anchor 261 is located in slot 902.Lower half 330 is adjacent inferior vertebra 40 and radial anchor 370 islocated in slot 904. Radial anchor 371 is located in slot 903.

In order to align superior vertebra 20 and inferior vertebra 40, upperhalf 340 and lower half 330 are aligned. A spanner is inserted intospanner slot 405 of implant 320. Set screw 350 is rotated to move lowerimplant half 330 anteriorly and upper implant half 340 posteriorally. Inone embodiment, for each complete 360 degrees turn of the set screw willmove lower half 330 1 mm with respect to upper when alignment of theimplant halves is complete, the threads in upper threaded collar 345 andin lower threaded collar 355 will align. Ideally, alignment of theimplant halves will align the vertebrae.

After alignment of the vertebrae, an interbody arthrodesis is performedon each side of implant 320 and between remaining distended disk 70. Thetechnique for interbody arthrodesis is surgeon's choice from those knowntechniques.

FIGS. 19A and 19B illustrate one embodiment of plate 540. Plate 540 isselected based on shape and size of individual patient's vertebrae. Inone embodiment, the height of plate 540 is between 2.5 cm and 7 cm andthe width of plate 540 is between 1.5 cm and 5 cm. Depth of plate 540 isbetween 0.2 cm and 1.5 cm. Plate 540 has front surface 541 facing ananterior side and back surface 542 facing a posterior side where backsurface 542 is slightly concave to approximate the curvature of inferiorvertebra 40 and superior vertebra 20.

Plate 540 includes plate nut hole 560 in its approximate center. Thefront diameter 543 of plate nut hole 560 on the anterior side of plate540 is between 0.65 cm and 3.4 cm while the back diameter 544 of platenut hole 560 on the posterior side of plate 540 is between 0.45 cm and2.5 cm.

Plate 540 also includes four holes 550. Each hole 550 should havediameter between about 1 mm and about 9 mm. But these diameters canvary. The plate is secured to the vertebra by stainless steel screws asknown in the art.

Preferably, plate 540 should be made of titanium or stainless steel.

FIG. 18 illustrates one embodiment of nut 500. Nut 500 has nut head 520which is elliptical. Diameter of nut head 520 is between 0.65 cm and 3.4cm preferably. Nut head 520 contains spanner holes 535. Nut body 510 hasdiameter of between 0.5 cm and 2.5 cm. The diameter of nut body 510should be approximately the same as diameter of implant body 346. Thelength of nut body 510 is between 0.2 cm and 6 cm. Nut 500 should beconstruction of titanium or stainless steel. Other rigid materials canbe used. Nut body 510 includes threaded hole 526. Threaded hole 526 isthreaded to match the threads of upper threaded collar 345 and lowerthreaded collar 355 on implant 320.

In use, to help secure implant 320 in position, nut 500 and plate 540are used, as illustrated in FIG. 20. Nut body 510 is placed throughplate nut hole 560. Nut thread 525 of threaded hole 526 is then alignedwith and threaded onto upper threaded collar 345 and lower threadedcollar 355. Nut 500 prevents implant upper half 340 and implant lowerhalf 330 from moving horizontally against each other.

Plate 540 is then properly aligned with the shape of superior vertebra20 and inferior vertebra 40. Corticocancellous screws 570 are placedinto each of the plate screw holes 550 and screwed into the respectivevertebrae by traditional techniques within the field. The difference indiameters between plate nut hole 560 from front surface 541 to backsurface 542 allows articulation of the bolt with respect to the plate,with front diameter 543 preferably larger than back diameter 544. Onceplate 540 is attached to superior vertebrae 20 and inferior vertebrae 40with screws 570, and is secured via nut 500 to implant 320 the deviceacts as a monolithic structure preventing rotational, lateral oranterior/posterior movement of vertebral bodies 20 and 40 with respectto each other, allowing ossification of said vertebral bodies.

Surgery is completed by standard anterior approach surgery techniquesand implant is in place.

In the event that adjustments need to be made to implant 320, screws570, nut 500 and plate 540 can be removed and set screw 350 adjustedwith any appropriate spanner head wrench. Nut 500, plate 540 and screws570 are then replaced.

FIGS. 21, 22A and 22B illustrate another preferred embodiment of thesaw. FIG. 21 shows saw 802 with mill bit 750. Saw 802 includes handle817 and conical section 814. Interior of handle 817 includes motor 860.Motor 860 is attached to mounting frame 808. Motor 860 is connected totransmission shaft 700. Switch 840 is integrated into handle 817 and isconnected to motor 860 through wire 850. Switch 840 activates anddeactivates motor 860. Motor 860 is connected to power source such as arechargeable lithium ion battery or another renewable power supply asknown in the art

Motor 860 rotates transmission shaft 700 between 15,000 to 20,000 rpm.In another preferred embodiment, motor 860 has variable speeds and speedof motor 860 is modulated through use of switch 840.

Conical section 814 is connected to handle post 811. Handle post 811integrally supports saw guide post 812. Saw guide post 812 isperpendicular to the longitudinal axis of saw 802. Handle post 811 isrigidly attached to spindle shaft 800. Shoulder 822 is positionedbetween handle post 811 and guide body 795. Guide body 795 is free torotate with respect to handle post 811 and spindle shaft 800.

Transmission hole 815 extends through handle 817, conical section 814,handle post 811 and spindle shaft 800.

Transmission shaft 700 extends through transmission hole 815.Transmission shaft 700 is kept in position within transmission hole 815by bushings 880. Transmission shaft 700 extends beyond spindle shaft 800and into transmission housing 725.

Guide body 795 has spindle hole 810 which transverses the longitudinalaxis of guide body 795. Spindle shaft 800 fits within spindle hole 810.Spindle hole 810 allows rotation of spindle shaft 800 about thelongitudinal axis of guide body 795. Transmission shaft 700 extendsthrough washer 670 and nut 680 into transmission housing 725.

FIG. 22A illustrates the mechanics inside transmission housing 725.Bearings 710 and 712 maintain position of transmission shaft 700 withintransmission housing 725 while allowing it to rotate. Transmission shaft700 terminates in bevel gear 735. Thrust bushing 709 is affixed betweenbevel gear 735 and bearing 712 and constrains the axial movement oftransmission shaft 700. Bevel gear 735 meshes with bevel gear 610creating 90 degree transmission. Other transmission schemes, such as aflexible cable, will suffice in other embodiments.

Bevel gear 610 is rigidly integrally connected to bearing shaft 620.Bearing shaft 620 is rigidly integrally connected to frustroconicalsection 637 which is rigidly integrally connected to jaws 650 of chuck660. Mill bit 750 is inserted into jaws 650. The position of chuck 660with respect to transmission housing 725 is maintained by bearings 740and 730 and thrust bushing 708. Mill bit 750 is parallel to saw guidepost 812.

FIGS. 23A and 23B are further illustrations of chuck 660. Bevel gear 610is integrally connected to bearing shaft 620. Bearing shaft 620 isintegrally connected to jaws 650. Jaws 650 are approximately cylindricalin shape with mill bit hole 882 removed which is same shape as end ofmill bit 750. Jaws 650 have set screw hole 640. Set screw hole 640 isthreaded to mate with set screw 630.

In one embodiment, mill bit hole 882 has flat surface 642 andsemicircular surface 641. Set screw hole 640 is centered along thelatitudinal axis of flat surface 642.

Referring to FIGS. 22A and 22B, mounting plate 720 is attached totransmission housing 725 through use of screws 722. Mounting plate 720has set screw hole 770. Set screw hole 770 allows access to set screw630 for locking mill bit 750 into chuck 660. Mounting plate 720 has bitstop 836 and mounting bracket 835.

Referring now to FIG. 22B, guide body 795 includes horizontal stop 780and vertical stop 790. Horizontal stop 780 extends from top 782 of guidebody 795 and has horizontal surface 787. Vertical stop 790 is alignedwith bottom 783 of guide body 795. Vertical stop 790 and horizontal stop780 cooperate with bit stop 836 to limit the rotation of thetransmission housing and the mill bit to 90 degrees between a verticalposition and a horizontal position.

When handle 817 is turned counter-clockwise with respect to thelongitudinal axis of guide body 795, bit stop 836 is rotatedcounterclockwise until bit stop 836 abuts saw guide vertical stop 790.Mill bit 750 will be substantially perpendicular to guide body 795 whenbit stop 836 abuts guide vertical stop 790. When handle 817 is rotatedclockwise with respect to the longitudinal axis of guide body 795, bitstop 836 will rotate clockwise until bit stop 836 abuts horizontal stop780. When bit stop 836 abuts horizontal stop 780, mill bit 750 will besubstantially parallel to guide body 795.

In use, mill bit 750 is inserted into mill bit hole 882. Set screw 630is advanced through set screw hole 770, into set screw hole 640 untilabuts mill bit 750. Saw 802 is then inserted into a distractor asdescribed in previous embodiment. Switch 840 activates motor 860 byconnecting it to a power source, which rotates transmission shaft 700and bevel gear 735. Rotation of bevel gear 735 rotates bevel gear 610and chuck 660, which causes mill bit 750 to rotate. Handle 817 ismanually rotated counterclockwise around the longitudinal axis of guidebody 795 which rotates mill bit 750 in relation to the longitudinal axisof guide body 795 and exposing mill bit 750 to vertebrae in order to cuta slot in the vertebra. After a slot has been cut, handle 817 ismanually rotated clockwise around the longitudinal axis of guide body795 until mill bit 750 is substantially parallel to latitudinal axis ofguide body 795. Switch 840 then deactivates motor 860. The procedure isrepeated for cutting additional slots in vertebra as previouslydescribed with manual saw embodiment.

Mill bit 750 has a diameter of between approximately 1 mm and 5 mm and alength of between 0.6 cm and 3.9 cm and corresponds to the size of theradial anchors of the implant being inserted between vertebra. Multiplesize mill bits are included and the appropriate size is inserted tocorrespond to size needed for the particular implant.

In some spondylolisthesis conditions, the relocation of vertebra mayeither be minor or unnecessary, however the natural tilt and locationbetween two adjacent vertebrae needs to be maintained and stabilized.For this type of condition, another embodiment of an implant andinstrumentation are used which includes a tapering to match the tilt ofthe vertebrae.

FIGS. 24A and 24B are illustrative of an additional preferred embodimentof a tapered implant. Implant 845 has an implant body 853 that istapered creating a frustroconical shape. Implant body 853 has implantbody front end 870 and back end 861. The cross-section of front end 870is circular. The cross-section of back end 861 is circular. Degree oftapering 875 is the degree by which the tapering occurs along implantbody 853 and ranges between approximately 2 and 10 degrees.

Implant body 853 has two halves, upper half 862 and lower half 864.Upper half 862 and lower half 864 meet at implant seam 855.

Implant body 853 has radial anchors 876 and 877 on upper half 862 andradial anchors 878 and 879 on lower half 864. Radial anchors 876, 877,878, and 879 are substantially perpendicular to implant seam 855. Radialanchors 878 and 876 have less surface area than radial anchors 877 and879, and are reduced in area to conform to a modified distractor asshown in FIG. 25. Other features of implant 845 are similar to thosepreviously described in other embodiment.

FIG. 25 is illustrative of other preferred embodiments for a distractorand impactor to be used with tapered implant 845. FIG. 25 illustratesimpactor 950 within distractor 940.

Distractor 940 has distractor arm 895 and distractor arm 892. Distractorarm 895 extends longitudinally from side 955 of distractor 940.Distractor arm 892 extends longitudinally from side 945 of distractor940. Distractor arm 895 has taper arm 890 which tapers both the top andbottom between an approximate 2 and 10 degree angle along thelongitudinal axis of distractor arm 895. Taper arm 897 on distractor arm892 tapers the height from both the top and the bottom between anapproximate 2 and 10 degree angle. Taper arm 897 includes distractorstop 910 and taper arm 890 has distractor stop 906. The remainingfeatures of distractor 940 are consistent with previously disclosedembodiment of distractor.

Impactor 950 has impactor head 911. The posterior end of impactor head911 has tapered end 898. Tapered end 898 has between approximately 2 and10 degrees of taper along the longitudinal axis of impactor head 911.Tapered end 898 ends in impactor seat 920 and on either side of impactorseat 920 are stop surfaces 930 and 931. The tapering of tapered end 898corresponds to the tapering of taper arm 890 and taper arm 897 such thatstop surfaces 930 and 931, when fully inserted, touch distractor stop906 and distractor stop 910 and do not extend beyond edges of distractorarms 892 or 895. The remaining features of impactor 950 are consistentwith previously disclosed embodiment of impactor.

As disclosed with prior embodiments, with the tapered implant system,the implant, distractor, impactor, and other parts necessary to completethe disclosed surgery have a variety of heights depending on the patientand the condition to be resolved.

1. A system for correcting alignment between two vertebrae caused byspondylolisthesis comprising: a distractor having a distractor body witha hollow channel along a distractor body longitudinal axis, an anteriorend, a posterior end having first a first distractor arm and a seconddistractor arm which extend from the distractor body in the direction ofthe distractor body longitudinal axis, the first distractor armextending parallel to the distractor body longitudinal axis having afirst distractor stop surface perpendicular to the distractor bodylongitudinal axis, the second distractor arm extending parallel to thedistractor body longitudinal axis having second distractor stop surfaceperpendicular to the distractor body longitudinal axis, a gap betweenthe first distractor stop surface and the second distractor stopsurface, a measurement scale along the first distractor arm, and atorque handle perpendicularly attached to the distractor body; animpactor having an impactor handle, an impactor body having an impactorlongitudinal axis, an impactor latitudinal axis, an impactor bodyanterior end, and an impactor body posterior end, the impactor handlebeing centered on the latitudinal axis of the impactor body anteriorend, an impactor seat centered along the latitudinal axis of theimpactor body posterior end; the impactor seat fitting within the gap onthe distractor; a gate having a gate longitudinal axis, a gatelatitudinal axis, an interior channel along the gate longitudinal axiswith a distractor end and a saw end, the distractor end having adistractor entrance to the interior channel and having a distractorstop, the saw end having a saw entrance to the interior channel, a topside, a bottom side, a right sidewall, a left sidewall, a first set ofguide slots extending from about the center of the right sidewall toabout the center of the bottom side and parallel to the saw end, asecond set of guide slots extending from about the center of the leftsidewall to about the center of the top side and parallel to the sawend, a first handle guide slot at about the center of the right sidewallextending along the right sidewall from the saw end and connecting tothe first set of guide slots and terminating in a first handle stop, asecond handle guide slot at about the center of the left sidewallextending along the left sidewall from the saw end and connecting to thesecond set of guide slots and terminating in a second handle stop, thefirst set of guide slots having a first set spacing and the second setof guide slots having a second set spacing, the first set spacingrelated to the second set spacing by a third set spacing; a saw with asaw longitudinal axis, the saw having a saw handle jointed to a spindleshaft, a saw guide body, and a saw guide post, the saw guide post joinedto the saw handle at an angle generally perpendicular to the sawlongitudinal axis, the saw guide body having a longitudinal spindle holecoaxial with the saw longitudinal axis, the spindle shaft rotativelymounted in the longitudinal hole, the saw guide body further having ahorizontal saw alignment stop and a vertical saw alignment stop, the sawhandle having a handle housing, a motor rigidly mounted in the handlehousing, a drive shaft connected to and driven by the motor, the driveshaft extending through a hole in the handle housing and the spindleshaft, a transmission housing rigidly attached to the spindle shaft, atransmission located within the transmission housing, the transmissionoperatively connected to the drive shaft and to a chuck, the chuckreleasably fixed to a mill bit, a mounting plate attached to thetransmission housing, the mill bit movable between a stoppage positiondictated by the mounting plate engagement with the horizontal sawalignment stop and an operational position dictated by the mountingplate engagement with the vertical saw alignment stop; an implant havinga first half having a first body with a first longitudinal axis, a firstthreaded collar, a first channel, a first mating interconnection, afirst outer surface and a first set of radial anchors, the first set ofradial anchors radially extending generally perpendicularly from thefirst outer surface, a second half having a second body with a secondlongitudinal axis, a second threaded collar, a second channel, a secondmating interconnection, a second outer surface and a second set ofradial anchors, the second set of radial anchors radially extendinggenerally perpendicularly from the second outer surface, the first halfand the second half slidably connected by the first matinginterconnection and the second mating interconnection, the first bodyand the second body connected to form an implant body, the firstthreaded collar and the second threaded collar connected to form animplant collar with a first thread pitch, the first channel and thesecond channel connected to form an implant channel, the first channelbeing threaded with a set of channel threads, a set screw having anoutside perimeter and a spanner slot, the outside perimeter beingthreaded with a set of set screw threads, the set screw located in theimplant channel, the set of channel threads in engagement with the setof set screw threads, the set of channel threads and the set of setscrew threads having a pre-determined relationship to allow the firsthalf to move a pre-determined distance in relation to the second halfwhen the set screw is rotated a pre-determined angle of rotation, thefirst set of radial anchors and the second set of radial anchors beinggenerally parallel; an inserter having a top half and a bottom half, thetop half further having a top longitudinal axis and a top mating guidealong the top longitudinal axis, the top half having a firstsemi-cylindrical section and a first semi-hexagonal section, the bottomhalf having a bottom longitudinal axis and a bottom mating channel alongthe bottom longitudinal axis, the bottom half having a secondsemi-cylindrical section and a second semi-hexagonal section, the tophalf and the bottom half slidingly connected along the top mating guideand the bottom mating channel creating a cylindrical section and ahexagonal section, the top half having a connection end, the connectionend having a threaded implant channel; the threaded implant channelhaving a second thread pitch; the first thread pitch matching the secondthread pitch; a guide block having a guide block longitudinal axis, aguide block top connected to guide block bottom, and a guide holecentered through the guide block longitudinal axis; a nut having a nuthead and a nut body, the nut body being generally perpendicular to thenut head, the nut body having a threaded hole, the threaded hole havinga third thread pitch; the first thread pitch matching the third threadpitch; and a plate having a plate nut hole, a plurality of plate screwholes, and a front, a back, and the plate nut hole having a frontdiameter and a back diameter.
 2. The system of claim 1 wherein the frontdiameter is larger than the back diameter.
 3. The system of claim 1wherein the first implant half further comprises a first set ofalignment marks and the second implant half further comprises a secondset of alignment marks and the first set of alignment marks align withthe second set of alignment marks when the first set of radial anchorsis parallel with the second set of radial anchors.
 4. The system ofclaim 1 wherein the first distractor arm includes a first distractorpoint guide having a first rounded surface and the second distractor armincludes a second distractor point guide having a first angled surface.5. The system of claim 1 wherein the nut head includes a set of spannerholes.
 6. The system of claim 1 wherein the gate has a visual indicatorindicating a gate orientation for the distractor.
 7. The system of claim1 wherein the measurement scale has a plurality of markings spaced 1 mmapart.
 8. The system of claim 1 wherein the impactor handle has acenterline which is parallel to a horizontal axis of the impactor body.9. The system of claim of claim 4 wherein the impactor seat has a secondrounded surface.
 10. A system of tools for inserting an implant forcorrecting a spondylolisthesis condition between two affected vertebraecomprising: a distractor having a distractor body with a hollow channelalong a distractor body longitudinal axis, an anterior end, a posteriorend having first a first distractor arm and a second distractor armwhich extend from the distractor body in the direction of the distractorbody longitudinal axis, the first distractor arm having a first taperingend and a first stop surface perpendicular to the distractor bodylongitudinal axis, the second distractor arm having a second taperingend and a second stop surface perpendicular to the distractor bodylongitudinal axis, the first tapering end and the second tapering endtapering in height by a set tapering degree, a gap between the firststop surface and the second stop surface, and a torque handle attachedto the distractor body; an impactor having a striking end, a posteriorend, and an impactor body, the impactor body having a tapering end, thetapering end tapering in height by the set tapering degree; the impactorfitting within the hollow channel of the distractor; a gate having agate longitudinal axis, a gate latitudinal axis, an interior channelalong the gate longitudinal axis with a distractor end and a saw end,the distractor end having a distractor entrance to the interior channeland having a distractor stop, the saw end having a saw entrance to theinterior channel, a top side, a bottom side, a right sidewall, a leftsidewall, a first set of guide slots extending from about the center ofthe right sidewall to about the center of the bottom side and parallelto the saw end, a second set of guide slots extending from about thecenter of the left sidewall to about the center of the top side andparallel to the saw end, a first handle guide slot at about the centerof the right sidewall extending along the right sidewall from the sawend and connecting to the first set of guide slots and terminating in afirst handle stop, a second handle guide slot at about the center of theleft sidewall extending along the left sidewall from the saw end andconnecting to the second set of guide slots and terminating in a secondhandle stop, the first set of guide slots having a first set spacing andthe second set of guide slots having a second set spacing, the first setspacing related to the second set spacing by a third set spacing; theanterior end of the distractor fitting within the distractor entranceand adjacent to the saw entrance; a saw with a saw longitudinal axis,the saw having a handle joined to a spindle shaft, the handle having ahandle housing, a motor rigidly mounted in the handle housing, a driveshaft connected to and driven by the motor, the drive shaft extendingthrough a hole in the handle housing and the spindle shaft, a saw guideprojection joined to the handle at an angle generally perpendicular tothe saw longitudinal axis, the saw guide body further having alongitudinal pivot hole coaxial with the longitudinal axis, the spindleshaft rotatively mounted in the longitudinal pivot hole, a transmissionhousing rigidly attached to the spindle shaft, a transmission locatedwithin the transmission housing, the transmission operatively connectedto the drive shaft and to a chuck, the chuck releasably fixed to a millbit, the transmission housing further comprising an index means forlimiting the rotation of the transmission housing with respect to theguide body, the mill bit movable between a stoppage position and anoperational position; the saw guide body fitting within the saw entranceof the gate and the hollow channel of the distractor; an implant adaptedto be fitted between the two affected vertebrae having a first halfhaving a first half longitudinal axis, a first half outer surface, and afirst joint and a second half having a second half longitudinal axis, asecond half outer surface, and a second joint, the first half and thesecond half connected by the first joint and the second joint forming animplant body, the implant body further having a frustroconical shape,the frustroconical shape tapered by the set tapering degree, the firsthalf having a first channel and the second half having a second channelsuch that when the first half and the second half are connected thefirst channel and the second channel form an implant chamber in theimplant body, a drive bolt located inside the implant chamber having afirst set of threads, the first channel being threaded, a second set ofthreads, the first half having a first set of radial anchors extendingsubstantially perpendicularly from the first half outer surface and thesecond half having a second set of radial anchors extendingsubstantially perpendicularly from the second half outer surface; thefirst set of threads engaging the second set of threads; an inserterhaving a top half and a bottom half, the top half having a toplongitudinal axis and a top joint along the top longitudinal axis, thebottom half having a bottom longitudinal axis and a bottom joint alongthe bottom longitudinal axis, the top half and the bottom half slidinglyconnected along the top joint and the bottom joint, the top half havinga connection end, the connection end releasably connectable to theimplant body; a nut having a nut head and a nut body, the nut body beingperpendicular to the nut head, the nut body having an implant hole,releasably connectable to the implant body; a plate connectable to thetwo affected vertebrae having a plate hole through which passes the nutbody.
 11. The system of claim 10 wherein the implant body furthercomprises a set of indexing marks on the first implant half and thesecond implant half.
 12. The system of claim 10 wherein the gate furthercomprises a pointing means for tactically discerning a direction ofinsertion.
 13. The system of claim 10 wherein the distractor furthercomprises a measurement scale along the first longitudinal extension.14. The system of claim 10 where the guide body further comprising ahorizontal blade stop and a vertical blade stop.
 15. The system of claim10 further comprising a set of gates wherein each gate in the set ofgates has a different third set spacing.
 16. The system of claim 10further comprising a set of distractors, wherein each distractor of theset of distractors has a unique height.
 17. The system of claim 10further comprising a set of impactors, wherein each impactor of the setof impactors has a unique height.
 18. The system of claim 10 furthercomprising a set of saw guide bodies, wherein each saw guide body of theset of saw guide bodies has a unique height.
 19. The system of claim 10further comprising a set of implants, each of the set of implant bodieshaving a unique diameter.
 20. The system of claim 10 wherein the settapering degree is a range from approximately 2 degrees to approximately10 degrees.